AbstractThe in vitro activities of 20 Strychnos alkaloids have been determined against three species of protozoa and the active compounds were then assessed for in vitro cytotoxic activity using KB cells. 3′,4′‐dihydrosambarensine was the most active against Plasmodium falciparum, and was relatively nontoxic to KB cells (cytotoxic/antiprotozoal ratio, 1474). Usambarensine displayed the most selectivity against Entamoeba histolytica while 3′,4′‐dihydrousambarensine was the most selective compound against Giardia intestinalis although the cytotoxic/antiprotozoal ratios (20.4 and 6.6 respectively) were less favourable than the above.